>
> Since I don't remember seeing any detailed description by a pure hobbyist regarding diy photoresist method of producing pcbs, I think this thread is a good place to put my 2 cnts.
>
> I've standardized on both the negative Riston and negative liquid photoresist methods for what I would describe as hobby application with decent process control. Sometimes I will give the Pulsar toner tranfer a go, but if you don't hit the sweet spot in the laminator, the toner won't hold and the pricey Pulsar materials are a loss.
>
> It's true that the laminator is a critical part of any of the above methods. I bought mine from Pulsar, but as mentioned previously, this is not a professional photoresist laminator with specially formulated polymer rollers to give a perfect heat/pressure profile. Anyway, I use the Pulsar laminator and limit my boards to 4x5 inches. Remember, I'm a hobbyist, and my need for board space is minimal. With a small board the laminator roller doesn't need a perfect heat/pressure profile across its entire span.
>
> I have most of my experience with Datak liquid negative photoresist. the Datak stuff is a KPR type of formula, so if you don't like KPR, you can stop reading now. From the posts here, I gather it's only available Stateside. Years ago I would use Datak reversal film on 1 to 1 published circuit artwork to create the negative film. Ok for DIP and through hole back in those days, but not good for smd nowadays. I have standardized on the following:
>
> 1. Using Datak negative photoresist
>
> I use an inkjet printer to create a positive at 9600 dpi. I then open up my darkroom for business (e.g reuse my electronics lab) , and print a negative from the positive transparency on litho film. BTW, it is true that AB litho film appears to be going out of production in the US and Europe. You can still purchase US stock from here http://ultrafineonline.com/ulhicoorlifi.html and here http://www.valleylitho.com/acatalog/Valley_Litho_Supply_WA_4_Premium_Line___Halftone_56.html along with the AB chemicals. My litho negatives are spectacularly detailed and contrast is 100% AS LONG AS I DON'T CREATE POURS! My inkjet printer is great at laying down traces up to 1/4" with good density. Beyond that, things go downhill and the whole process is for naught. If you're a member of this group I needn't go into cleanliness of the copper clad and work environment required, or how to obtain same. Anyway, the Datak instructions at http://www.philmore-datak.com/datakneg.html are adequate. I will surmise that along with not liking the need to make a quality negative of the artwork, diy'rs probably don't get the spraying of the boards down to a science. You do have to heat the board to 120 - 140F before spraying. I spray the board at a 45deg. angle from 4-6in until there is a sheen, then I rotate 45deg. and respray. There are those who warn of too much resist applied. I think they actually have been shooting themselves in the foot for years with that warning. Spray enough to get a sheen from the resist. There may be a spray pattern at that point, but after the second spray at 45deg. there should be no spray pattern with an adequate application. I then put the board(s) into a skillet and cover at 140F for 20 minutes to dry the coating (all done with bug light or red light). You'll have to repeat the spray and bake for each two sided board.
>
> I have a desklamp with 2 F15T8 black light lamps which I use for exposure. I have a Datak printing frame. The Datak printing frame is quite good at holding the transparency in contact with the litho film, and also, later, holding a sensitized board in contact with the negative. The 15min. in the instruction sheet for board exposure works for me. However, as I think someone here has mentioned, you should let the lamps burn for at least 4 minutes before use, to get their output up to a steady level. Development is performed with a very pungent aromatic hydrocarbon so the instructions regarding adequate ventilation should be followed strictly. I prefer the dry film photoresist method described below, but I have to use this process with liquid photoresist when using thick boards (about .8mm) that I need to have heavy components (transformers and or large inductors) mounted on. The thick boards won't pass through the laminator for applying film photoresist. You can do a lot of pushing, and possibly get a board to pass over the roller, but I'm sure the laminator will eventually get excessive wear, there is a good chance the roller will develop a permanent impression, as well. You can also wind up bunching up / tearing the resist film (first hand experience)
> Etching has been well treated in this group, and I will say nothing about it.
>
> 2. Dry Film Photoresist
>
> When using .5mm thick, or less copper clad, I use dry film photoresist since this thickness of board will pass through the laminator.
>
> Dry film photoresist is available Stateside from www.thinktink.com/products/Photoresist.asp. The smallest amount (1ft by 50ft.) is pricey for a hobbyist, (over $100US) but should last for years if kept refrigerated, and there is enough to make hundreds of 4x5 inch boards, so the price per board is less than 35 cents, disregarding wastage. Handling photoresist film, by hand, without preproduction equipment, is like fighting with a piece of roll wax paper. It's a challenge, but for small boards, I can manage to strip the backing off, and get the photoresist onto the board. The most important technique to settle the photoresist smoothly to the pc board is to SPRAY THE BOARD WITH WATER. After laying the photoresist down on the board, use a rubber photo roller, or photo squeegee to work out the bubbles that invariably get trapped under the film. When making a two sided board, where you will be folding over the film, it's important that you cut the film width less than the width of the board. If you don't, the top and bottom films will bond together at the edges, preventing you from squeezing the bubbles out. Once you have a nice smooth application of the film to board, pass the board through the laminator, twice. Let the board cool for 15 minutes. Exposure should be determined with a Stouffer tablet (Google Riston and Stouffer). In my case, with two F15T8's 15 inches away, 8 minutes works well. BTW, to ensure sharp traces, you should place mirrored mylar behind the bulbs in the shape of a parabola, or some approximation, thereof. Think and Tinker goes into great detail on the truly proper way to collimate your UV source, but my mylarized desklamp has been good enough for sharp msop, soic, and tssop leads.
>
> By standardizing on the negative photoresist, liquid and film, I can simply pull a film from my litho library and and have the flexibility of choosing either method 1 or 2 above, as needed. Also, if you have access to the original Datak printed instructions it is brought out that the negative liquid resist has much greater shelf life than positive. Having to mail order from across the country, and pay shipping for every parcel, I prefer to minimize those transactions.
>
> BTW, one of the biggest challenges to keeping cost of diy pcb fabrication down, is finding reasonably priced copper clad. The cost from electronics outlets is astronomical! Ebay has been good to me, in this area.
>
> Hope this helps the strictly hobby group of diy folks on this thread.
>
> Stan
> --- In Homebrew_PCBs@yahoogroups.com, Harvey White <madyn@> wrote:
> >
> > On Mon, 26 Dec 2011 20:32:02 -0000, you wrote:
> >
> > >Hi,
> > >
> > >it's been years since I made my first circuit boards the old fashioned way, carefully tracing over the artwork with a sheet of carbon paper underneath onto the bare copper board and retracing again over the pattern left from the carbon paper using an etch resist pen and then using a #11 xacto to gently scribe any excess ink from the edges of the traces, touch up with pen, scribe, etc. until perect and then etch.
> >
> > I never got that to work.
> > >
> > >ok that was 30 years ago and I want to make some new boards now so looking at products ranging from DIY hobby to industrial production, youtube videos and websites I am in a better position to understand the processes now. basically from what I gather the first step is the one with the most variation, applying the etch resist to the board. etching is still pretty much the same all around.
> > >
> >
> > DIY is one thing, professional gets nasty.
> >
> > >there are 2 ways to go, either positive or negative photoresist,
> >
> > also toner transfer, which can be surprisingly decent.
> > >
> > >the former seems more straight forward considering the artwork is unchanged, but the chemicals to apply positive resist are expensive and not as readily available I am discovering.
> > >
> >
> > Take your word, presensitized boards are expensive, say 6 to 8 USD for
> > a 4 x 6 board.
> >
> > >There is a discontinued positive resist spray that was made by MG Chemical, and various liquid positive like Kodak KPR, and POSITIV 20 photoresist lacquer spray available by mail order from UK distributors. These all need to be applied in dark room conditions and fully cured before developing, possibly with heat from an oven.
> > >the nice thing I think is that no laminating machine is needed, since looking into that I find that "hot roller" is the way to go and that can get expensive.
> > >
> >
> > Avoid KPR like the plague. Works really well, but nasty chemicals,
> > really.....
> >
> > Problem with these is that unless you manage to get the coating even,
> > the exposure can vary a bit.
> >
> >
> > >
> > >next is the dry film negative that must be applied with a laminator, I see many videos showing DIYers running boards through the laminators several times in an attempt to compensate for low or uneven heat, something a more expensive 4 Hot Roller laminator (Tamerica / Tashin TCC6000) would be needed for even light production.
> >
> > I hear good results if you are careful.
> >
> > >
> > >when comparing the 2 methods it's possible to see pros and cons in both, positive must have a dedicated darkroom to work and negative is an investment into equpiment, namely a reasonable quality laminator that new might run over $400
> >
> > negative may need that same darkroom. However, a bathroom with some
> > towels across the door bottom can be just fine. I wouldn't worry
> > about the cost of the darkroom that much.
> >
> > >
> > >both need uv exposure but the latter need less power so maybe the cost is offset somewhat not having to absolutly have UV.
> >
> > Generally, three or four Blacklight tubes will do well enough, unless
> > you use something that needs shortwave UV (which gets nasty, really).
> >
> > Longwave is not all that bad, tubes are easy enough. The MG chemicals
> > uses pretty much 6500 degrees K daylight fluorescents. Slightly
> > difficult to find, but not expensive.
> >
> > >
> > >then it comes to what brand of dry negative resist?
> >
> > no ideas here.
> >
> > >
> > >there are several including:
> > >
> > >MG Chemical
> > >
> > >Dupont Riston
> > >
> > >Kolon
> > >
> > >eBay nameless brands, etc.
> > >
> > >and then there are different types, thichnesses intended for different processes, electroplating, sandblasting, etc.
> > >
> > >I'm skipping the part where the transparency is made, guessing that would be fine just bringing the pcb file to Kinko's or an Office Box store on a flash drive, or buying at least a 600dpi, maybe even 1200dpi laser black and white printer, ok for cad art, a scanner also for magazine or other art. either pos or neg transparency for either spray on/chemical or dry film, that I get.
> >
> > Not really, the more opaque the negative, the better you get.
> > Sometimes you need red ink from an inkjet, laser may not be
> > sufficient. Some experimentation is needed. Not opaque enough, you
> > start to expose the wrong regions.
> >
> > Ideal would be a photolith film, which is pretty much opaque black and
> > transparent. Sadly, Kodak Photolith is not made (IIRC) and it still
> > requires a good photoplotter (ideally), otherwise it's negative on
> > transparency.
> >
> > >
> > >so my questions then are,
> > >
> > >anyone with any experience either with the positive resist chemicals and/or the various brands of negative dry resist films?
> >
> > Only the MG boards and KPR.
> >
> >
> > >
> > >I'm looking for information beyond manufacturers claims and DIY videos or websites to help in comparison of these 2 photoresist methods and the various processes and products required.
> > >
> > >Many thanks and happy holidays to all,
> >
> > And to you.
> >
> > Harvey
> >
> > >
> > >Robert
> > >
> > >
> > >
> > >
> > >
> > >------------------------------------
> > >
> > >Be sure to visit the group home and check for new Links, Files, and Photos:
> > >http://groups.yahoo.com/group/Homebrew_PCBsYahoo! Groups Links
> > >
> > >
> > >
> >
>